1. Field of the Invention
The present invention relates to an image forming apparatus having a configuration for preventing faulty stacking of recording sheets.
2. Related Background Art
A conventional image forming apparatus will be described with reference to the drawings. FIG. 9 is a view showing an entire conventional image forming apparatus and FIG. 10 is a view for explaining a movement of a sheet at a sheet discharging portion.
In recent years, the image forming apparatus has been widely used such as a copying machine, a printer or a facsimile, which has a configuration based on a copying machine. However, a recent rapid prevalence of a personal computer has been bringing the configuration to be mainly based on the printer.
When the image forming apparatus has a configuration based on a printer, as shown in FIG. 9, it is typical to provide a sheet discharge tray 106 on which sheets recorded are discharged above the image forming portion 102 and to discharge the sheets with their image-formed surfaces downward (facedown) so as to be in page order. In the case of using the apparatus as a copying machine, it is possible to form it to be an inside apparatus sheet discharging type copying machine by providing an image reading portion (reader portion) spaced above the discharge tray 106.
In this image forming apparatus, a toner image is transferred onto the sheet P fed from a sheet discharging portion 101 at the image forming portion 102, and fixed by having the sheet P on which the toner image has been transferred passed through a fixing portion 103. Then, the sheet P is generally discharged from a pair of first discharging rollers 104, 105 to the sheet discharge tray 106.
In case of fitting a post-treatment apparatus 109 such as a sorter or a finisher to the image forming apparatus, the recording sheet P is conveyed in a reverse direction (a direction of the post-treatment apparatus 109) with its rear end nipped by the pair of first discharging rollers 104, 105, and fed from a pair of second discharging rollers 107, 108 provided in the image forming apparatus to a conveying roller in the post-treatment apparatus 109 to be subjected to a predetermined post-treatment.
In an image forming apparatus called a complex machine serving functions of a copying machine, a printer and a facsimile together, by fitting the post-treatment apparatus 109 as shown in FIG. 9, it is obviously possible to sort the sheets such that a copy output sheet is sorted into a bin 109a, a printer output sheet into a bin 109b and a facsimile output sheet into a bin 109c to be output.
However, the above described image forming apparatus has following problems.
As described above, when the post-treatment apparatus 109 is mounted on the image forming apparatus, the front end of the sheet P fed to the post-treatment apparatus 109 is discharged on the sheet discharge tray 106, and then, conveyed in the direction of the post-treatment apparatus 109 by reversely rotating the pair of first discharging rollers 104, 105 at a predetermined timing to turn over the conveying direction.
In this case, when the recording sheet P is to be fed to the post-treatment apparatus 109 as shown in FIG. 10, the front end of the recording sheet P (or the rear end when being conveyed in the direction of the post-treatment apparatus) trails in contact with the recording sheet already stacked on the sheet discharge tray 106 so that there is a possibility of the sheet already discharged being bent or damaged. In addition, the sheet P is discharged with the image formed surface downward (so-called, facedown) so that such trailing is likely to cause the image-formed surface to be rubbed and thereby to be contaminated.
In order to prevent such lowering of stacking ability, when the sheet conveyed in the direction of the post-treatment apparatus 109 is discharged on the sheet discharge tray 106, the sheet is temporality discharged onto a position different from the sheet discharge tray 106, or a spare tray is arranged for only turning over the sheet. Adopting these configurations, however, further requires a space into which the sheet is temporarily discharged or a component such as the spare tray, thereby raising an apparatus cost and making the apparatus larger in size.
The present invention is achieved in view of the above-mentioned problems and has as its object to provide an image forming apparatus which improves the stacking ability of sheets and prevents contamination of an image formed surface at a low cost. The image forming apparatus comprises: a frame; a first conveying path through which the sheet on which the image is formed by the image forming means is conveyed; a sheet discharge tray provided outside the frame and onto which the sheet conveyed through the first conveying path is discharged so as to be accommodated on the discharge tray; a first sheet discharging roller rotatable in a direction of discharging the sheet onto the sheet discharge tray and in a reverse direction thereof; and a second conveying path extending downwardly inside the frame from the first sheet discharging roller as a first end, with a section thereof formed in a substantially S-shaped; the second conveying path conveying the sheet conveyed in the direction of discharging from the first conveying path onto the sheet discharge tray by the first sheet discharging roller and pulled in the frame by reversely rotating the first sheet discharging roller during discharging.